The immune system and stroke: from current targets to future therapy.

Stroke is a major cause of morbidity and mortality worldwide. Despite the intensive search for new therapies, hundreds of agents targeting various pathophysiological mechanisms have failed clinical trials, and the thrombolytic agent tissue plasminogen activator is currently the only FDA-approved medication for the treatment of acute ischemic stroke. The immune system is involved in all stages of stroke, from the pathogenesis of risk factors to neurotoxicity, to tissue remodeling and repair. There is a bidirectional interaction between the brain and the immune system, with stroke-induced immunosuppression and subsequent infection a principal source of patient mortality. Newer work also points to a role for the gut microbiota in the immune response to stroke, while clinical sequelae such as dementia might now also be explained in immune terms. However, the exact roles of innate and adaptive components have not been fully elucidated, with studies reporting both detrimental and beneficial functions. Time is a key determinant in defining whether immunity and inflammation are neuroprotective or neurotoxic. The local inflammatory milieu also has a clear influence on many proposed treatments. This review examines the individual components of the immune response to stroke, highlighting the most promising future stroke immunotherapies.

Impaired B cells survival upon production of inflammatory cytokines by HIV-1 exposed follicular dendritic cells.

BACKGROUND: Follicular dendritic cells (FDCs) are important components in the organization of germinal centers in lymphoid tissue where, following antigen presentation, B cells differentiate into memory B cells. The possibility of establishing primary cell lines from FDCs isolated from lymphoid tissue paved the way for characterization of FDC biological properties. We exposed primary FDC cell lines to HIV-1 strains in vitro and studied changes in the chemo-attractive properties of FDCs and release of inflammatory cytokines. RESULTS: FDC lines expressed several known and putative HIV-1 receptors; viral genome was amplified in HIV-1 exposed FDCs which released low levels of p24 HIV-1 protein in culture supernatants, but were not definitely proven to be productively infected. Exposure of FDCs to HIV-1 strains did not change the expression of markers used to characterize these cells. HIV-1 exposed FDCs, however, changed the expression of chemo-attractants involved in cell recruitment at inflammatory sites and increased the production of several inflammatory cytokines. The inflammatory milieu created upon HIV-1 exposure of FDCs led to impaired B cell survival in vitro and reduced Ig production. CONCLUSIONS: FDC lines exposed to different HIV-1 strains, although not able to support productive HIV-1 replication, show an increased production of inflammatory cytokines. Our in vitro model of interactions between HIV-1 exposed FDC lines and B cells suggest that exposure of FDCs to HIV-1 in vivo can contribute to inflammation within germinal centers and that this pathological event may impair B cell survival and contribute to impaired B cell responses during HIV-1 infection.

New Insights into IL-10 Dependent and IL-10 Independent Mechanisms of Regulatory B Cell Immune Suppression.

Regulatory B (Breg) cells are important regulators of immune responses and in recent years our understanding of their phenotypical and functional characteristics has improved considerably. Initially all suppressive capabilities of Breg cells were attributed to the actions of the anti-inflammatory cytokine interleukin (IL)-10 secreted by Breg cells. Recent studies however, highlight additional and novel mechanisms that influence both the expansion of Breg cells and their capacity to suppress immunity. Here we provide an overview of the complexity of Breg cell populations and address the newly discovered IL-10 independent mechanisms of Breg cell expansion and immune-suppression.

Ligation of TLR7 on CD19(+) CD1d(hi) B cells suppresses allergic lung inflammation via regulatory T cells.

B cells have been described as having the capacity to regulate cellular immune responses and suppress inflammatory processes. One such regulatory B-cell population is defined as IL-10-producing CD19(+) CD1d(hi) cells. Previous work has identified an expansion of these cells in mice infected with the helminth, Schistosoma mansoni. Here, microarray analysis of CD19(+) CD1d(hi) B cells from mice infected with S. mansoni demonstrated significantly increased Tlr7 expression, while CD19(+) CD1d(hi) B cells from uninfected mice also demonstrated elevated Tlr7 expression. Using IL-10 reporter, Il10(-/-) and Tlr7(-/-) mice, we formally demonstrate that TLR7 ligation of CD19(+) CD1d(hi) B cells increases their capacity to produce IL-10. In a mouse model of allergic lung inflammation, the adoptive transfer of TLR7-elicited CD19(+) CD1d(hi) B cells reduced airway inflammation and associated airway hyperresponsiveness. Using DEREG mice to deplete FoxP3(+) T regulatory cells in allergen-sensitized mice, we show that that TLR7-elicited CD19(+) CD1d(hi) B cells suppress airway hyperresponsiveness via a T regulatory cell dependent mechanism. These studies identify that TLR7 stimulation leads to the expansion of IL-10-producing CD19(+) CD1d(hi) B cells, which can suppress allergic lung inflammation via T regulatory cells.

Frequency and phenotype of B cell subpopulations in young and aged HIV-1 infected patients receiving ART.

BACKGROUND: Aged individuals respond poorly to vaccination and have a higher risk of contracting infections in comparison to younger individuals; whether age impacts on the composition and function of B cell subpopulations relevant for immune responses is still controversial. It is also not known whether increased age during HIV-1 infection further synergizes with the virus to alter B cell subpopulations. In view of the increased number of HIV-1 infected patients living to high age as a result of anti-retroviral treatment this is an important issue to clarify. RESULTS: In this work we evaluated the distribution of B cell subpopulations in young and aged healthy individuals and HIV-1 infected patients, treated and naïve to treatment. B cell populations were characterized for the expression of inhibitory molecules (PD-1 and FcRL4) and activation markers (CD25 and CD69); the capacity of B cells to respond to activation signals through up-regulation of IL-6 expression was also evaluated. Increased frequencies of activated and tissue-like memory B cells occurring during HIV-1 infection are corrected by prolonged ART therapy. Our findings also reveal that, in spite of prolonged treatment, resting memory B cells in both young and aged HIV-1 infected patients are reduced in number, and all memory B cell subsets show a low level of expression of the activation marker CD25. CONCLUSIONS: The results of our study show that resting memory B cells in ART-treated young and aged HIV-1 infected patients are reduced in number and memory B cell subsets exhibit low expression of the activation marker CD25. Aging per se in the HIV-1 infected population does not worsen impairments initiated by HIV-1 in the memory B cell populations of young individuals.

A mineral extract from red algae ameliorates chronic spontaneous colitis in IL-10 deficient mice in a mouse strain dependent manner.

Inflammatory bowel disease is an urgent public health problem with a high incidence in developed countries. Alterations of lifestyle or dietary interventions may attenuate the disease progression and increase the efficacy of current therapies. Here we tested the effect of chronic supplementation with a mineral extract from red marine algae - rich in calcium (34%), magnesium, phosphorus, selenium and other trace minerals - in a clinically relevant model of spontaneous enterocolitis, interleukin (IL)-10(-/-) mice. The mineral extract was administered in the drinking water of Il10(-/-) mice on C57BL/6 J and BALB/c strain backgrounds for 25 weeks commencing from 3 to 4 weeks of age. The mineral extract ameliorated the spontaneous development of colitis and severity of disease in Il10(-/-) mice on a C57BL/6 J background. Mineral extract-treated Il10(-/-) C57BL/6 J strain mice had significantly reduced mortality, circulating levels of serum Amyloid A and reduced colonic tissue damage. In contrast, comparable treatment of Il10(-/-) mice on a BALB/c background with the mineral extract did not alter the course of colitis. These data demonstrate that chronic supplementation with a natural mineral extract selectively ameliorates spontaneous mild-moderate colitis in Il10(-/-) mice on a C57BL/6 J, but does not attenuate more moderate-severe colitis in BALB/c strain animals.

The synthetic cannabinoid R(+)WIN55,212-2 augments interferon-ß expression via peroxisome proliferator-activated receptor-α.

We have demonstrated that R(+)WIN55,212-2, a synthetic cannabinoid that possesses cannabimimetic properties, acts as a novel regulator of Toll-like receptor 3 (TLR3) signaling to interferon (IFN) regulatory factor 3 (IRF3) activation and IFN-ß expression, and this is critical for manifesting its protective effects in a murine multiple sclerosis model. Here we investigated the role of peroxisome proliferator-activated receptor-α (PPARα) in mediating the effects of R(+)WIN55,212-2 on this pathway. Data herein demonstrate that the TLR3 agonist poly(I:C) promotes IFN-ß expression and R(+)WIN55,212-2 enhances TLR3-induced IFN-ß expression in a stereoselective manner via PPARα. R(+)WIN55,212-2 promotes increased transactivation and expression of PPARα. Using the PPARα antagonist GW6471, we demonstrate that R(+)WIN55,212-2 acts via PPARα to activate JNK, activator protein-1, and positive regulatory domain IV to transcriptionally regulate the IFN-ß promoter. Furthermore, GW6471 ameliorated the protective effects of R(+)WIN55,212-2 during the initial phase of experimental autoimmune encephalomyelitis. Overall, these findings define PPARα as an important mediator in manifesting the effects of R(+)WIN55,212-2 on the signaling cascade regulating IFN-ß expression. The study adds to our molecular appreciation of potential therapeutic effects of R(+)WIN55,212-2 in multiple sclerosis.

A role for TLR4 in Clostridium difficile infection and the recognition of surface layer proteins.

Clostridium difficile is the etiological agent of antibiotic-associated diarrhoea (AAD) and pseudomembranous colitis in humans. The role of the surface layer proteins (SLPs) in this disease has not yet been fully explored. The aim of this study was to investigate a role for SLPs in the recognition of C. difficile and the subsequent activation of the immune system. Bone marrow derived dendritic cells (DCs) exposed to SLPs were assessed for production of inflammatory cytokines, expression of cell surface markers and their ability to generate T helper (Th) cell responses. DCs isolated from C3H/HeN and C3H/HeJ mice were used in order to examine whether SLPs are recognised by TLR4. The role of TLR4 in infection was examined in TLR4-deficient mice. SLPs induced maturation of DCs characterised by production of IL-12, TNFα and IL-10 and expression of MHC class II, CD40, CD80 and CD86. Furthermore, SLP-activated DCs generated Th cells producing IFNγ and IL-17. SLPs were unable to activate DCs isolated from TLR4-mutant C3H/HeJ mice and failed to induce a subsequent Th cell response. TLR4⁻/⁻ and Myd88⁻/⁻, but not TRIF⁻/⁻ mice were more susceptible than wild-type mice to C. difficile infection. Furthermore, SLPs activated NFκB, but not IRF3, downstream of TLR4. Our results indicate that SLPs isolated from C. difficile can activate innate and adaptive immunity and that these effects are mediated by TLR4, with TLR4 having a functional role in experimental C. difficile infection. This suggests an important role for SLPs in the recognition of C. difficile by the immune system.

Intra-peritoneal sRAGE treatment induces alterations in cellular distribution of CD19(+), CD3 (+) and Mac-1 (+) cells in lymphoid organs and peritoneal cavity.

Receptor for advanced glycation end products (RAGE) is a pattern recognition receptor that binds a variety of pro-inflammatory ligands. Its soluble form, sRAGE, can compete for ligand binding and thereby have an anti-inflammatory effect. We have recently reported that sRAGE also exerts pro-inflammatory and chemotactic properties suggesting a dual role for sRAGE in immune modulation. Our present aim was to analyse the immunomodulatory properties of sRAGE in vivo with respect to acquired immunity. Naive mice were treated intra-peritoneally with sRAGE and cells from peritoneal lavage, spleens and bone marrow were examined. Mice treated with sRAGE displayed an increased leucocyte count in the peritoneal cavity, enlarged spleens and increased cellularity compared with vehicle-treated animals. Furthermore, sRAGE-treated mice had a significantly increased frequency and number of CD19(+) B cells in spleen and a reduced frequency of CD19(+) B cells in bone marrow compared with controls. Functionally, splenocytes from sRAGE-treated mice showed elevated IgG production and up to a four-fold increased IgM secretion compared with control animals and produced significantly higher levels of interleukin-10, interferon-γ and interleukin-6 in response to lipopolysaccharide stimulation. Our results suggest that sRAGE has immunomodulatory properties, since intra-peritoneal administration of sRAGE into healthy mice leads to rearrangements in cellular composition in the bone marrow and spleen. Moreover, the administration of sRAGE directs B cells into the spleen and towards differentiation. Our novel findings indicate that sRAGE exerts an effect on the cells of adaptive immunity.

Blockade of B7-H1 (programmed death ligand 1) enhances humoral immunity by positively regulating the generation of T follicular helper cells.

T follicular helper (T(FH)) cells are critical initiators in the development of T cell-dependent humoral immunity and the generation of protective immunity. We demonstrate that T(FH) cell accumulation and Ab production are negatively regulated by B7-H1 (programmed death ligand 1) in response to both helminth infection and active immunization. Following immunization of B7-H1(-/-) mice with keyhole limpet hemocyanin or helminth Ags, there is a profound increase in induction of T(FH) cells as a result of increased cell cycling and decreased apoptosis relative to wild-type mice. The increase in T(FH) cells in the absence of B7-H1 was associated with significant elevations in Ag-specific Ig response. Cotransfer experiments in vivo demonstrated that B7-H1 expression on B cells was required for negatively regulating T(FH) cell expansion and production of Ag-specific Ig. Treatment of immunized wild-type mice with anti-B7-H1 or anti-programmed death 1 mAbs, but not anti-B7-DC, led to a significant expansion of the T(FH) cell population and an enhanced Ag-specific Ig response. Our results demonstrate that the coinhibitory B7-H1/programmed death 1 pathway can limit the expansion of T(FH) cells and constrain Ag-specific Ig responses. This finding has direct implications for investigations examining the feasibility of therapeutically manipulating this pathway and reveals new insights into the regulation of the humoral immune response.

Current perspectives on mesenchymal stromal cell therapy for graft versus host disease.

Graft versus host disease (GvHD) is the clinical condition in which bone marrow-derived mesenchymal stromal cells (MSCs) have been most frequently studied. In this review, we summarize the experience from clinical trials that have paved the way to translation. While MSC-based therapy has shown an exceptional safety profile, identifying potency assays and disease biomarkers that reliably predict the capacity of a specific MSC batch to alleviate GvHD has been difficult. As GvHD diagnosis and staging are based solely on clinical criteria, individual patients recruited in the same clinical trial may have vastly different underlying biology, obscuring trial outcomes and making it difficult to determine the benefit of MSCs in subgroups of patients. An accumulating body of evidence indicates the importance of considering not only the cell product but also patient-specific biomarkers and/or immune characteristics in determining MSC responsiveness. A mode of action where intravascular MSC destruction is followed by monocyte-efferocytosis-mediated skewing of the immune repertoire in a permissive inflammatory environment would both explain why cell engraftment is irrelevant for MSC efficacy and stress the importance of biologic differences between responding and nonresponding patients. We recommend a combined analysis of clinical outcomes and both biomarkers of disease activity and MSC potency assays to identify patients with GvHD who are likely to benefit from MSC therapy.

Lipid rafts are disrupted in mildly inflamed intestinal microenvironments without overt disruption of the epithelial barrier.

Intestinal epithelial barrier disruption is a feature of inflammatory bowel disease (IBD), but whether barrier disruption precedes or merely accompanies inflammation remains controversial. Tight junction (TJ) adhesion complexes control epithelial barrier integrity. Since some TJ proteins reside in cholesterol-enriched regions of the cell membrane termed lipid rafts, we sought to elucidate the relationship between rafts and intestinal epithelial barrier function. Lipid rafts were isolated from Caco-2 intestinal epithelial cells primed with the proinflammatory cytokine interferon-γ (IFN-γ) or treated with methyl-ß-cyclodextrin as a positive control for raft disruption. Rafts were also isolated from the ilea of mice in which colitis had been induced in conjunction with in vivo intestinal permeability measurements, and lastly from intestinal biopsies of ulcerative colitis (UC) patients with predominantly mild or quiescent disease. Raft distribution was analyzed by measuring activity of the raft-associated enzyme alkaline phosphatase and by performing Western blot analysis for flotillin-1. Epithelial barrier integrity was estimated by measuring transepithelial resistance in cytokine-treated cells or in vivo permeability to fluorescent dextran in colitic mice. Raft and nonraft fractions were analyzed by Western blotting for the TJ proteins occludin and zonula occludens-1 (ZO-1). Our results revealed that lipid rafts were disrupted in IFN-γ-treated cells, in the ilea of mice with subclinical colitis, and in UC patients with quiescent inflammation. This was not associated with a clear pattern of occludin or ZO-1 relocalization from raft to nonraft fractions. Significantly, a time-course study in colitic mice revealed that disruption of lipid rafts preceded the onset of increased intestinal permeability. Our data suggest for the first time that lipid raft disruption occurs early in the inflammatory cascade in murine and human colitis and, we speculate, may contribute to subsequent disruption of epithelial barrier function.

Hydroxylase inhibition attenuates colonic epithelial secretory function and ameliorates experimental diarrhea.

Hydroxylases are oxygen-sensing enzymes that regulate cellular responses to hypoxia. Transepithelial Cl(-) secretion, the driving force for fluid secretion, is dependent on O(2) availability for generation of cellular energy. Here, we investigated the role of hydroxylases in regulating epithelial secretion and the potential for targeting these enzymes in treatment of diarrheal disorders. Ion transport was measured as short-circuit current changes across voltage-clamped monolayers of T(84) cells and mouse colon. The antidiarrheal efficacy of dimethyloxallyl glycine (DMOG) was tested in a mouse model of allergic disease. Hydroxylase inhibition with DMOG attenuated Ca(2+)- and cAMP-dependent secretory responses in voltage-clamped T(84) cells to 20.2 ± 2.6 and 38.8 ± 6.7% (n=16; P≤0.001) of those in control cells, respectively. Antisecretory actions of DMOG were time and concentration dependent, being maximal after 18 h of DMOG (1 mM) treatment. DMOG specifically inhibited Na(+)/K(+)-ATPase pump activity without altering its expression or membrane localization. In mice, DMOG inhibited agonist-induced secretory responses ex vivo and prevented allergic diarrhea in vivo. In conclusion, hydroxylases are important regulators of epithelial Cl(-) and fluid secretion and present a promising target for development of new drugs to treat transport disorders.

Cancer Immunotherapy with Immune Checkpoint Inhibitors-Biomarkers of Response and Toxicity; Current Limitations and Future Promise.

Immune checkpoint inhibitors are monoclonal antibodies that are used to treat over one in three cancer patients. While they have changed the natural history of disease, prolonging life and preserving quality of life, they are highly active in less than 40% of patients, even in the most responsive malignancies such as melanoma, and cause significant autoimmune side effects. Licenced biomarkers include tumour Programmed Death Ligand 1 expression by immunohistochemistry, microsatellite instability, and tumour mutational burden, none of which are particularly sensitive or specific. Emerging tumour and immune tissue biomarkers such as novel immunohistochemistry scores, tumour, stromal and immune cell gene expression profiling, and liquid biomarkers such as systemic inflammatory markers, kynurenine/tryptophan ratio, circulating immune cells, cytokines and DNA are discussed in this review. We also examine the influence of the faecal microbiome on treatment outcome and its use as a biomarker of response and toxicity.

Activation of human invariant natural killer T cells with a thioglycoside analogue of α-galactosylceramide.

Activation of CD1d-restricted invariant NKT (iNKT) cells with the glycolipid α-galactosylceramide (α-GalCer) confers protection against disease in murine models, however, clinical trials in humans have had limited impact. We synthesized a novel thioglycoside analogue of α-GalCer, denoted α-S-GalCer, and tested its efficacy for stimulating human iNKT cells in vitro. α-S-GalCer stimulated cytokine release by iNKT cells in a CD1d-dependent manner and primed CD1d(+) target cells for lysis. α-S-GalCer-stimulated iNKT cells induced maturation of monocyte-derived dendritic cells into antigen-presenting cells that released IL-12 and small amounts of IL-10. The nature and potency of α-S-GalCer and α-GalCer in human iNKT cell activation were similar. However, in contrast to α-GalCer, α-S-GalCer did not activate murine iNKT cells in vivo. Because of its enhanced stability in biological systems, α-S-GalCer may be superior to α-GalCer as a parent compound for developing adjuvant therapies for humans.

Phenotype and function of CD25-expressing B lymphocytes isolated from human umbilical cord blood.

BACKGROUND: We have shown that approximately 30% of human peripheral blood B-cells express CD25. B cells expressing CD25 display a mature phenotype belonging to the memory B-cell population and have a better proliferative and antigen-presenting capacity. The aim of the present study was to characterize the CD25-expressing subset of B cells in human cord blood. MATERIAL AND METHODS: Mononuclear cell fraction from human cord blood (n=34) and peripheral adult blood (n=22) was sorted into CD20+CD25+ and CD20+CD25- B-cell populations. Phenotype and function of these B-cell populations were compared using flow cytometry, proliferation, cytokine production, and immunoglobulin secretion. RESULTS: CD25-expressing B cells are a limited population of cord blood mononuclear cells representing 5% of the CD20+ B cells. They are characterised by high expression of CD5 in cord blood and CD27 in adult blood. CD25-expressing B cells express a functional IL-2 receptor and high levels of CC-chemokine receptors and spontaneously produce antibodies of IgG and IgM subclass. CONCLUSIONS: CD25 expression is a common denominator of a specific immunomodulatory B-cell subset ready to proliferate upon IL-2 stimulation, possibly ready to migrate and home into the peripheral tissue for further differentiation/action.

Regulatory B cells prevent and reverse allergic airway inflammation via FoxP3-positive T regulatory cells in a murine model.

BACKGROUND: Parasitic helminth infections of humans have been shown to suppress the immune response to allergens. Experimentally, infection of mice with the helminth Schistosoma mansoni prevents allergic airway inflammation and anaphylaxis via IL-10 and B cells. OBJECTIVE: To identify and characterize the specific helminth-induced regulatory B-cell subpopulation and determine the mechanism by which these regulatory B cells suppress allergic airway inflammation. METHODS: IL-10-producing B cells from the spleens of helminth-infected mice were phenotyped, isolated, and transferred to ovalbumin-sensitized mice, and their ability to modulate allergic airway inflammation was analyzed. RESULTS: S mansoni infection induced IL-10-producing CD1d(high) regulatory B cells that could prevent ovalbumin-induced allergic airway inflammation following passive transfer to ovalbumin-sensitized recipients. The capacity of regulatory B cells to suppress allergic airway inflammation was dependent on the expression of CD1d, and they functioned via an IL-10-mediated mechanism. Regulatory B cells induced pulmonary infiltration of CD4(+)CD25(+) forkhead box protein 3(+) regulatory T cells, independent of TGF-beta, thereby suppressing allergic airway inflammation. Regulatory B cells that were generated ex vivo also suppressed the development of allergic airway inflammation. Furthermore, the transfer of regulatory B cells reversed established airway inflammation in ovalbumin-sensitized mice. CONCLUSION: We have generated in vivo and ex vivo a regulatory B cell that can prevent or reverse allergen-induced airway inflammation via regulatory T cells.

Impact of chemokine C-C ligand 27, foreskin anatomy and sexually transmitted infections on HIV-1 target cell availability in adolescent South African males.

We compared outer and inner foreskin tissue from adolescent males undergoing medical male circumcision to better understand signals that increase HIV target cell availability in the foreskin. We measured chemokine gene expression and the impact of sexually transmitted infections (STIs) on the density and location of T and Langerhans cells. Chemokine C-C ligand 27 (CCL27) was expressed 6.94-fold higher in the inner foreskin when compared with the outer foreskin. We show that the density of CD4+CCR5+ cells/mm2 was higher in the epithelium of the inner foreskin, regardless of STI status, in parallel with higher CCL27 gene expression. In the presence of STIs, there were higher numbers of CD4+CCR5+ cells/mm2 cells in the sub-stratum of the outer and inner foreskin with concurrently higher number of CD207+ Langerhans cells (LC) in both tissues, with the latter cells being closer to the keratin surface of the outer FS in the presence of an STI. When we tested the ability of exogenous CCL27 to induce T-cell migration in foreskin tissue, CD4 + T cells were able to relocate to the inner foreskin epithelium in response. We provide novel insight into the impact CCL27 and STIs on immune and HIV-1 target cell changes in the foreskin.

Immunomodulatory Therapeutic Strategies in Stroke.

The role of immunity in all stages of stroke is increasingly being recognized, from the pathogenesis of risk factors to tissue repair, leading to the investigation of a range of immunomodulatory therapies. In the acute phase of stroke, proposed therapies include drugs targeting pro-inflammatory cytokines, matrix metalloproteinases, and leukocyte infiltration, with a key objective to reduce initial brain cell toxicity. Systemically, the early stages of stroke are also characterized by stroke-induced immunosuppression, where downregulation of host defences predisposes patients to infection. Therefore, strategies to modulate innate immunity post-stroke have garnered greater attention. A complementary objective is to reduce longer-term sequelae by focusing on adaptive immunity. Following stroke onset, the integrity of the blood-brain barrier is compromised, exposing central nervous system (CNS) antigens to systemic adaptive immune recognition, potentially inducing autoimmunity. Some pre-clinical efforts have been made to tolerize the immune system to CNS antigens pre-stroke. Separately, immune cell populations that exhibit a regulatory phenotype (T- and B- regulatory cells) have been shown to ameliorate post-stroke inflammation and contribute to tissue repair. Cell-based therapies, established in oncology and transplantation, could become a strategy to treat the acute and chronic stages of stroke. Furthermore, a role for the gut microbiota in ischaemic injury has received attention. Finally, the immune system may play a role in remote ischaemic preconditioning-mediated neuroprotection against stroke. The development of stroke therapies involving organs distant to the infarct site, therefore, should not be overlooked. This review will discuss the immune mechanisms of various therapeutic strategies, surveying published data and discussing more theoretical mechanisms of action that have yet to be exploited.